High amounts of tumour‐associated macrophages (TAMs) and hyaluronan (HA) correlate with tumour aggressiveness in breast cancer, but the relationship between these parameters is unclear. The aim of this study was to assay the numbers of TAMs in 278 human breast cancer cases, and their correlations with HA‐related factors, clinical variables, and outcome.

The immunoreactivities for CD163 and CD68 were considered as indicators for M2‐like and all TAMs, respectively. The numbers of TAMs were counted in at least four hot spots, and averaged to represent the numbers of TAMs in each section. In the statistical analyses, the numbers were graded as either low or high according to the median. High numbers of TAMs correlated with a high tumour HA content, HA synthases, CD44 positivity, and poor outcome. The number of CD163‐positive cells represented a strong independent prognostic factor. There was also a significant correlation between obesity and a high number of CD163‐positive cells.

Concurrent increases in TAMs and HA in breast cancer indicate that the accumulation of HA facilitates macrophage infiltration and inflammatory responses during human breast cancer progression.